1. Field
Embodiments disclosed herein generally relate to a magnetic disk device employing a microwave assisted magnetic recording (MAMR) head.
2. Description of the Related Art
Over the past few years, MAMR has been studied as a recording method to improve the areal density of a magnetic read/write device, such as a hard disk drive (HDD). MAMR enabled magnetic recording heads utilize a spin torque oscillator (STO) for generating a microwave (high frequency AC magnetic field). When the magnetic field from the write head is applied and current is conducted to the STO, the STO oscillates and may provide an AC magnetic field to the recording medium. The AC magnetic field may reduce the coercive force of the recording medium, thus high quality recording by MAMR may be achieved. Typically the STO includes a spin polarization layer (SPL), a field generation layer (FGL) and an interlayer disposed between the SPL and the FGL. The STO generates high frequency magnetic fields, or microwaves, as a result of the transfer of spin torque from the SPL through the interlayer to the FGL, and the in-plane high speed rotation of the magnetization of the FGL serves as the in-plane free layer.
In MAMR, optimizing STO frequency is difficult since the frequency margin for high gain is low. A typical MAMR head has a large distribution in STO frequency because the STO frequency depends on the writer dimensions as well as the STO dimensions. Conventionally the current applied to the STO flows in one-way direction, and STO bias optimization is not effective for optimizing STO frequency because the dependency of frequency on STO bias has a step-like behavior.
Therefore, there is a need in the art for an improved recording head for MAMR.